1. Field of the Invention
The present invention generally relates to an effector imparting a sound effect to an input tone by executing a plurality of microprograms within a limited processing capacity of the effector, and outputting the tone imparted with the sound effect. The present invention also relates to a machine readable medium storing a program for controlling the effector.
2. Description of Related Art
Conventional effectors that impart a desired sound effect to an input tone and that output the resultant tone use a DSP (Digital Signal Processor), which manipulates an input signal by repeatedly executing a microprogram on a sampling frequency basis of the input signal. Such a DSP is generally composed of a program memory for storing a microprogram, a waveform computing unit for executing this microprogram to manipulate an input signal and to output the manipulated signal, and a control register for holding data necessary for executing the microprogram.
An effector has also been developed that uses a multi-microprogram DSP (hereafter, referred to as a multi-MP-DSP). The multi-MP-DSP stores plural microprograms in an internal program memory, and the waveform computing unit executes these microprograms concurrently. The effector of this type can impart a different desired effect to each of the input signals of plural channels.
It is necessary for the multi-MP-DSP to execute two or more microprograms in one sampling period of an input signal. However, the sampling frequency of the input signal varies dependently on required tone qualities. Generally, for a tone signal such as music sound, the sampling frequency is set to 44.1 kHz. If the number of steps of each microprogram is 128, the operating clock frequency of the waveform computing unit of the DSP needs to be 44,100xc3x97128=5,644,800 Hz or higher in order to execute one microprogram in one sampling period. Therefore, concurrent execution of n microprograms in one sampling period requires to provide a waveform computing unit that operates at a clock frequency n times as high as the above-mentioned frequency.
The multi-MP-DSP may have plural blocks for concurrently executing one microprogram, these blocks operating independently of each other. Therefore, the throughput of the DSP must be based on each of these blocks as long as the plural microprograms are allocated to these blocks separately, even if the plural microprograms are the same in content. In other words, regardless of the contents of the microprograms to be used, the operating clock frequency needs to be multiplied by n in the multi-MP-DSP. Obviously, provision of plural waveform computing units in the DSP for concurrent processing may lower the necessary operating clock frequency; however, this constitution requires a throughput n time as high as that required by the execution of one microprogram like the case described above.
Currently, if the sampling frequency of an input signal is 44.1 kHz, the number of microprograms executable by one multi-MPDSP is at most about two or three. Normally, the number of microprograms exceeding this limitation cannot be allocated to the blocks of the multi-MP-DSP. Therefore, many effects exceeding the limit cannot be simultaneously used. Even when only effects in the number lower than the above-mentioned limit are used, if the total number of effects to be used from starting of tone reproduction to ending thereof exceeds the above-mentioned limit, all necessary effects cannot be allocated to the blocks beforehand.
It is therefore an object of the present invention to provide an effector apparatus capable of setting many effects at a time and a machine readable medium storing a program for controlling this effector apparatus.
According to the invention, an effector apparatus is constructed for imparting acoustic effects to an audio signal by executing microprograms. The inventive apparatus comprises processing means having a process capacity only sufficient to execute a limited number of microprograms in parallel to each other to create acoustic effects in processing of the audio signal, setting means operable for individually selecting the microprograms and for setting a level of the acoustic effect to be created by each of the selected microprograms so that each microprogram is made inactive when the acoustic effect thereof is set to a zero level and otherwise is made active when the acoustic effect is set to other than the zero level, and controlling means for controlling the processing means to execute each active microprogram within the limited number while skipping execution of each inactive microprogram to thereby achieve efficient use of the process capacity of the processing means.
Preferably, the setting means comprises means operable in advance of the processing of the audio signal for presetting an excess number of microprograms over the limited number for selective use of the microprograms, and means operable during the course of the processing of the audio signal for dynamically setting the level of the acoustic effect to be created by each microprogram so as to reduce the number of active ones of the preset microprograms within the limited number.
Preferably, the setting means includes means manually operable during the processing of the audio signal for selecting a desired one of the audio effects and for changing the level of the selected audio effect.
Preferably, the processing means includes memory means having a memory capacity sufficient to load the limited number of the microprograms for execution thereof, and the controlling means comprises unloading means operative during the processing of the audio signal for unloading the inactive microprogram from the memory means, and loading means operative during the processing of the audio signal for loading the active microprogram into the memory means in place of the unloaded inactive microprogram so that the microprograms to be executed during the processing of the audio signal can be changed within the limited number.
Preferably, the processing means includes memory means having a memory capacity sufficient to store all of the microprograms including active ones and inactive ones, and the controlling means comprises means for selectively retrieving the active microprograms from the memory means for execution by the processing means.
Preferably, the apparatus further comprises alarm means operative when the number of the active microprograms exceeds the limited number for indicating an alarm such that the setting means can be manually operated to change at least one of the active microprograms to an inactive one by setting the acoustic effect to be created by the active microprogram to the zero level.
According to the invention, a machine readable medium is for use in an effector apparatus having a CPU and a digital signal processor for imparting acoustic effects to an audio signal by executing microprograms. The medium contains instructions executable by the CPU for causing the effector apparatus to perform the steps of operating the digital signal processor having a process capacity only sufficient to execute a limited number of microprograms in parallel to each other to create acoustic effects in processing of the audio signal, individually selecting the microprograms during the course of the processing of the audio signal, setting a level of the acoustic effect to be created by each of the selected microprograms so that each microprogram is made inactive when the acoustic effect thereof is set to a zero level and otherwise is made active when the acoustic effect is set to other than the zero level, and controlling the digital signal processor to execute each active microprogram within the limited number while skipping execution of each inactive microprogram to thereby achieve efficient use of the process capacity of the digital signal processor.